Piezo actuators are being ever more widely used. They are used for example in fluid metering devices which can be embodied for example as an injection valve for dispensing fuel for internal combustion engines.
Ever more stringent legal requirements in relation to permissible pollutant emissions of internal combustion engines which are disposed in motor vehicles make it necessary to take various measures through which the pollutant emissions are reduced. One approach in this case is to reduce the pollutant emissions created during the process of air/fuel mixture combustion. The formation of soot in particular is heavily dependent on the preparation of the air/fuel mixture in the respective cylinder of the internal combustion engine.
In order to obtain a very good mixture preparation, fuel is increasingly dispensed at very high pressure. In the case of diesel engines fuel pressures amount to up to 2000 bar, in the case of petrol engines they amount to around 200 bar. These types of application increasingly involve injection valves with a piezo actuator used as their actuator. The outstanding feature of piezo actuators is their very short response times. These types of injection valve are thus suitable if necessary for dispensing fuel several times within an operating cycle of a cylinder of the internal combustion engine.
An especially good mixture preparation can be achieved if one or more pre-injections, also known as pilot injections, are performed before a main injection, with the mass of fuel to be dispensed for each pilot injection possibly being very small. A precise activation of the injection valves is very important, especially in these cases.